1. Field of the Invention
The present invention relates to a device at the output side of a gas turbine for conducting the combustion gases to a heat exchanger or into a bypass. The device includes guide surfaces arranged in the branching area between the heat exchanger and the bypass.
2. Description of the Related Art
The operation of gas turbines which are followed by a heat exchanger usually requires during start-up of the gas turbine that the heat exchanger is bypassed by means of a bypass. Flap valves are used for optionally guiding the combustion gases to the heat exchanger or to the bypass. These flap valves are arranged in the duct leading to the heat exchanger which duct extends in the flow direction of the combustion gases and the flap valves are arranged in the duct leading to the bypass which duct extends perpendicularly to the flow direction of the combustion gases. These ducts have extremely large cross-sectional areas, for example 20 square meters or more.
The result obtained from the operation of these devices are not satisfactory. The flaps which are closed during the bypass operation and lead to the heat exchanger begin to leak after a very short time and the flaps are frequently damaged until they are destroyed. A reason for this is that the hot combustion gases impact directly on the closed flap with high kinetic energy. In addition, a pulsation occurs in the combustion gases which has a low vibration frequency and substantially contribute to rendering the flaps prematurely useless.
In another known arrangement, the combustion gases are not conducted along a straight line from the gas turbine to the heat exchanger. Rather, to the horizontal ducts at the output side of gas turbine is connected a perpendicularly extending duct portion to which, in turn, are connected a horizontally extending duct which leads to the heat exchanger and a duct which extends in perpendicular direction and leads to the bypass. Stationary guide surfaces are arranged in the deflection region between the horizontally extending ducts from the gas turbine and the perpendicularly extending portion. These guide surfaces facilitate the deflection of the horizontally arriving flow of the combustion gases into an approximately perpendicularly extending direction.
The arrangement described above also has significant disadvantages. The guide surfaces are continuously subjected, i.e., during the start-up as well as during the continuous operation with the heat exchanger, to the pressure of the hot combustion gases and, thus, the guide surfaces wear quickly. The heat exchanger cannot be arranged in the same plane as the gas turbine, but rather the heat exchanger must be raised relative to the gas turbine. Accordingly, the heat exchanger requires an extensive substructure and a greater height of the building in which the unit is set up than is necessary normally. Finally, the guide surfaces constitute a significant resistance to the flow of the combustion gases from the gas turbine. This resistance is continuous, i.e., it does not only occur during the start-up of the turbine.
It is, therefore, the primary object of the present invention to provide a device of the above-described type which is simple and inexpensively avoids the above-mentioned problems.